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Shear Stress Partitioning of Vegetal Elements

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  032132,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.14010) @2003
Authors:   Anita M. Thompson, Bruce N. Wilson
Keywords:   Vegetation, Shear Stress, Hot-film Anemometry, Overland Flow

Vegetation is an important large-scale roughness element that partitions the total shear force into a portion acting on the soil surface and a portion acting on large-scale roughness. The fraction acting on the soil surface is directly involved in subsequent particle detachment. This study investigated the shear partition for idealized vegetation in overland flow. Vegetation was represented by rigid circular cylinders and idealized elements with differences in the rate of change in upstream frontal area with flow depth. Detailed spatial and temporal particle shear measurements were made using a unique hydraulic flume and hot-film anemometry. Three uniformly spaced element densities were investigated: 1, 4, and 9 elements per 0.145 m2. Element width to spacing ratios ranged from 0.04 to 0.20. Average particle shear ranged from 0.73 to 2.27 Pa, form shear from 0.12 to 7.94 Pa, and total shear from 1.1 to 9.1 Pa. Over the range of densities studied, particle shear accounted for 13% to 89% of the total shear, indicating that complete surface coverage is not required to significantly reduce the shear stress acting on soil particles. Existing shear partitioning theory provided reasonable representation of the observed shear partition.

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